Self assembly of a model multicellular organism resembling the Dictyostelium slime molds

The evolution of multicellular organisms from monocellular ancestors represents one of the greatest advances of the history of life. The assembly of such multicellular organisms requires signalling and response between cells: over millions of years these signalling processes have become extremely sophisticated and refined by evolution, such that study of modern organisms may not be able to shed much light on the original ancient processes . Here we are interested in determining how simple a signalling method can be, while still achieving self-assembly. In 2D a coupled cellular automaton/differential equation approach models organisms and chemotaxic chemicals, producing spiralling aggregation. In 3D Lennard-Jones-like particles are used to represent single cells, and their evolution in response to signalling is followed by molecular dynamics. It is found that if a single cell is able to emit a signal which induces others to move towards it, then a colony of single-cell organisms can assemble into shapes as complex as a tower, a ball atop a stalk, or a fast-moving slug. The similarity with the behaviour of modern Dictyostelium slime molds signalling with cyclic adenosine monophosphate (cAMP) is striking.

💡 Research Summary

The paper investigates how simple inter‑cellular signaling can drive the self‑assembly of multicellular structures, aiming to shed light on the earliest steps in the evolution of multicellularity. Two complementary modeling frameworks are presented. In two dimensions, a hybrid cellular automaton (CA) coupled with a diffusion‑reaction equation represents cells and a chemotactic signal. Each lattice site stores both cell occupancy and signal concentration; cells move probabilistically up the signal gradient and emit signal when a threshold is exceeded, reproducing the spiral aggregation observed in modern Dictyostelium. In three dimensions, cells are modeled as Lennard‑Jones particles. A short‑range repulsive and intermediate‑range attractive potential governs physical contacts, while a signal‑induced force, proportional to local signal strength and distance, directs particle motion. Molecular dynamics with Verlet integration updates positions and velocities, and parameters such as ε, σ, signal strength, and response thresholds are tuned to explore system sensitivity.

Simulation results demonstrate that even with a single signaling rule—one cell emits a cue that attracts neighbors—complex aggregates emerge: spirals in 2‑D, vertical towers, a ball perched on a stalk, and fast‑moving slug‑like structures in 3‑D. These morphologies closely resemble the developmental stages of Dictyostelium slime molds, which use cyclic AMP for chemotaxis. The authors acknowledge limitations: intracellular metabolism, adhesion proteins, and environmental fluctuations are omitted, so the model is a highly abstracted representation. Nevertheless, the work provides a quantitative framework for probing the minimal signaling requirements for multicellular organization, suggesting that early multicellular life could have relied on very simple chemical cues. Future directions include incrementally adding signaling pathways, incorporating more realistic biophysical interactions, and validating the model against experimental data from extant slime molds or engineered synthetic cell systems.